<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        .search {
            width:300px;
            height: 30px;
            margin: 100px auto;
            position: relative;

        }
        .search input {
            width:200px;
            height:25px;
            
        }
        .search label {
            font-size: 12px;
            color:#ccc;
            position: absolute;
            top:8px;
            left:20px;
            cursor: text;
        }
    </style>
    <script>
        window.onload = function(){
            function $(id){return document.getElementById(id);}
            //oninput 大部分浏览器支持  检测用户表单输入内容
            //onpropertychange  ie678  检测用户表单输入内容
            $("txt").oninput = function(){
                if(this.value == " ")
                {
                    $("message").style.display = "block";
                }
                else
                {
                    $("message").style.display = "none";

                }
            }
            $("txt").onblur = function () {
                this.value = "";
                $("message").style.display = "block";
            }
        }
    </script>
</head>
<body>
<div class="search">
    <input type="text" id="txt"/>
    <label for="txt" id="message">必败的国际大牌</label>
</div>
</body>
</html>